Use of topography to direct assembly of block copolymers in grapho-epitaxial applications

ABSTRACT

A method is provided for forming a patterned topography on a substrate. The substrate is provided with features formed atop that constitute an existing topography, and a template for directed self-assembly (DSA) is formed surrounding the exposed topography. Further to the method, the exposed template surfaces are chemically treated. In one embodiment, the surfaces are treated with a hydrogen-containing reducing chemistry to alter the surfaces to a less oxidized state. In another embodiment, the surfaces are coated with a first phase of a block copolymer (BCP) to render the surfaces more attractive to the first phase than prior to the coating. The template is then filled with the BCP to cover the exposed topography, and then the BCP is annealed within the template to drive self-assembly in alignment with the topography. Developing the annealed BCP exposes a DSA pattern immediately overlying the topography.

The present application claims the benefit of and priority to U.S.Provisional Patent Application Nos. 61/893,275 and 61/893,277, eachfiled on Oct. 20, 2013, the disclosures of which are hereby incorporatedby reference herein in their entirety.

FIELD OF THE INVENTION

This invention relates to Directed Self-Assembly (DSA) of blockcopolymers (BCPs) and, more specifically, the use of grapho-epitaxy andoptionally chemo-epitaxy to drive the assembly of a BCP forsemiconductor patterning.

BACKGROUND OF THE INVENTION

The industry is running out of cost-effective ways to make smallpatterns in integrated circuit (IC) designs, especially hole structures.FIG. 1 illustrates schematically the need for such small holestructures. An array of lines 10 form a topography 20 on a substrate.The lines 10 need to be cut in a typical design, for example, a 10 nmnode design. Square-shaped holes 12 and rectangle-shaped holes 14 wouldbe patterned to allow access to the lines 10 for cutting. As the area ofthe entire pattern shrinks, smaller holes 12, 14 must be patterned, andthe space between holes gets tighter as well. Historically, lithographicapplications have been able to print all of these holes in a singleprint. However, currently, multiple exposure passes are required toprint the different holes because they are so close together and sosmall, and by the time the 10 nm node arrives, it is likely that as manyas four masks will be required to print even this simple geometry.

Block copolymers (BCPs) are being investigated for their use in makingfine patterns because they can thermodynamically form very small domainsof regular structures currently used in semiconductor patterning (e.g.,cylinder or line/space patterns). Typically, in these systems, theassembly of the BCP is directed by an external driving force. One suchmethod for directing the BCP assembly is through the use of physicaltemplates. However, there is a need for methods for directing theassembly of BCPs that enable greater control of the interfaces of theblocks to allow for more precise creation of the exact shapes needed tomake fine circuit patterns.

SUMMARY OF THE INVENTION

A method is provided for forming a patterned topography on a substrate.The substrate is provided with features formed atop that constitute anexisting topography, and a template for directed self-assembly (DSA) isformed surrounding the exposed topography. Further to the method, theexposed template surfaces are chemically treated. The template is thenfilled with the BCP to cover the exposed topography, and then the BCP isannealed within the template to drive self-assembly in alignment withthe topography. Developing the annealed BCP exposes a DSA patternimmediately overlying the topography.

In one embodiment, treating the exposed template surfaces alters atleast one surface property thereof. For example, the treatment mayrender the exposed template surfaces less attractive to a first phase ofthe block copolymer (BCP) compared to the exposed template surfacesprior to the treatment. By way of further example, when the exposedtemplate surfaces are oxidized during the formation of the template, thesurfaces may be treated with a hydrogen-containing reducing chemistry toalter the surfaces to a less oxidized state. The annealing of the blockcopolymer (BCP) within the template then drives self-assembly of theblock copolymer (BCP) with the first phase of the block copolymer (BCP)in alignment with the topography.

In another embodiment, the surfaces are coated with a first phase of ablock copolymer (BCP) to render the surfaces more attractive to thefirst phase than prior to the coating. The annealing of the blockcopolymer (BCP) within the template then drives self-assembly of theblock copolymer (BCP) with a second phase of the block copolymer (BCP)in alignment with the topography. In a further embodiment, prior tocoating with a first phase of a block copolymer, a direct currentsuperposition (DCS) treatment of the exposed template surfaces may beconducted to apply a layer of silicon to the exposed template surfaces,followed by exposing the layer of silicon on the exposed templatesurfaces to an oxygen-containing environment to oxidize the exposedtemplate surfaces. The coating then comprises a brush polymer of OH andthe first phase of a block copolymer (BCP).

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the presentinvention and, together with a general description of the inventiongiven above, and the detailed description of the embodiments givenbelow, serve to explain the principles of the present invention.

FIG. 1 is a schematic depiction of a line array with hole patterning forcutting the lines.

FIG. 2 schematically depicts formation of a graphical template over thearray of FIG. 1.

FIGS. 3A-3L depict in schematic cross-sectional view an embodiment of amethod for patterning a topography on a substrate using directedself-assembly.

FIG. 4 is a perspective view of the template of FIG. 2 used in asimulation study.

FIG. 5 is a plot of images in the simulation study taken along line 5-5of FIG. 2 for different surface interaction parameters.

FIGS. 6A-6B are 3-dimensional views of a DSA pattern, formed without andwith a topography in the template.

FIG. 7 is a top schematic view of a template overlying a topography witha DSA pattern tethered to the topography.

FIGS. 8A-8C are top schematic views of a method for tethering a DSApattern to a topography according to an embodiment.

DETAILED DESCRIPTION

Methods using grapho-epitaxy and chemo-epitaxy to drive the assembly ofa block copolymer for semiconductor patterning are disclosed in variousembodiments. However, one skilled in the relevant art will recognizethat the various embodiments may be practiced without one or more of thespecific details or with other replacement and/or additional methods,materials, or components. In other instances, well-known structures,materials, or operations are not shown or described in detail to avoidobscuring aspects of various embodiments of the present invention.

Similarly, for purposes of explanation, specific numbers, materials, andconfigurations are set forth in order to provide a thoroughunderstanding. Nevertheless, the embodiments of the present inventionmay be practiced without specific details. Furthermore, it is understoodthat the illustrative representations are not necessarily drawn toscale.

Reference throughout this specification to “one embodiment” or “anembodiment” or variation thereof means that a particular feature,structure, material, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention, butdoes not denote that they are present in every embodiment. Thus, theappearances of the phrases such as “in one embodiment” or “in anembodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the invention.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments. Various additional layers and/or structures may be includedand/or described features may be omitted in other embodiments.

Additionally, it is to be understood that “a” or “an” may mean “one ormore” unless explicitly stated otherwise.

Various operations will be described as multiple discrete operations inturn, in a manner that is most helpful in understanding the invention.However, the order of description should not be construed as to implythat these operations are necessarily order dependent. In particular,these operations need not be performed in the order of presentation.Operations described may be performed in a different order than thedescribed embodiment.

Various additional operations may be performed and/or describedoperations may be omitted in additional embodiments.

As described above, one method for directing the BCP assembly is throughthe use of physical templates. Another method is to build a chemicalactivity difference into the substrate so that one or both blocks of theBCP will align with the preferred substrate. In all such integrations,the key to good block copolymer assembly is the interaction of the blockcopolymer with the surfaces that it comes into contact with. Whetherchemo-epitaxy or grapho-epitaxy is used, the interaction of the BCP withboth the substrate and the sidewalls that it comes into contact withwill determine how it chooses to self-assemble. In accordance with theinvention, methods for directing the assembly of block copolymers aredisclosed that enable greater control of the interfaces of the blocks toallow for more precise creation of the exact shapes needed to make finecircuit patterns.

FIG. 2 schematically illustrates simplification of this process usingDSA. A graphical template 30 is formed over the topography 20 of FIG. 1to provide the location for holes 12 (three shown) that can be used tocut the lines 10. The holes 12 that would require multiple patterningare now being created through 1) patterning of a template 30 and 2)using this template 30 to place the holes 12 that will allow access tocut the lines 10. In addition to the template 30, and in accordance withembodiments of the invention, the directed assembly of the holes 12 isaugmented by utilizing the topography 20. Specifically, if thetopography 20 has or is treated in such a way that its chemical activityfavors the assembly of cylinders 32 on top of it, then the holes 12 canbe anchored to the topography 20. Thus, the invention is a DSAapplication that uses a hybrid grapho/chemo epitaxy approach. It isgraphical in that it uses the guiding template 30, and it is chemical inthat it uses the surface energy of the topography 20 to further augmentthe placement of the holes 12.

The following is a more detailed discussion of two different embodimentsof the invention that utilize this approach of using aspects of bothgrapho-epitaxy and chemo-epitaxy to drive the assembly of the BCP inspecific locations. In both embodiments, chemical treatment of atopography may be used to drive the assembly of a block copolymer withina graphical template. This specific technology is used within an overallwafer flow to generate the desired structures. However, it may beappreciated that the chemo-epitaxy aspect may be achieved withoutchemical treatment, such as by selecting materials for the topographyand template that provide the chemical differences inherently that drivethe assembly.

In the first embodiment, depicted in schematic cross-sectional view inFIGS. 3A-3L, an array of features, specifically lines 10, has beenpatterned on a substrate 18, such as a semiconductor wafer, to provide astarting topography 20, as shown in FIG. 3A, and the desire is to cutthese lines 10 in specific locations. To that end, in FIG. 3B, aplanarization layer 22 is applied to planarize the topography 20.Planarization layer 22 may be, for example, a spin-on carbon layer. Theplanarization layer 22 will ultimately form the template for thegrapho-epitaxy aspect of the invention. Next, as shown in FIG. 3C, ananti-reflective coating (ARC) layer 24, such as a silicon ARC, is coatedon top of the planarization layer 22. It may be understood that the ARClayer 24 may not by itself act as an antireflective coating, but rather,is more generically a second layer that acts in combination with theplanarization layer to provide a dual-layer bottom ARC (BARC) 26.Nonetheless, the second layer (layer 24) may be referred to as an ARClayer for the reason that it provides the antireflective properties whencombined with the first layer (planarization layer 22). The thicknessesand optical properties of these layers, which form the dual-layer BARC26, are tailored so that the substrate reflectivity is minimized.

A layer of radiation-sensitive material, e.g., photoresist 28, iscoated, as shown in FIG. 3D, and patterned (imaged) on top of thisdual-layer BARC 26, as shown in FIG. 3E, and the photoresist image issubsequently transferred into the planarization layer 22 throughtraditional reactive ion etching (RIE) processing, as shown in FIG. 3F(the photoresist 28 and ARC layer 24 are also removed) thereby formingthe template 30 in the planarization layer 22. The depth of etching intothe planarization layer 22 may be complete, so as to expose an uppersurface of the underlying substrate 18, or partial, so as to leave aportion of the planarization layer 22 at the bottom of the template 30.In either case, surface portions 36 of the lines 10 are exposed, so asto reveal an exposed topography 20 surrounded by the template 30.

The next step, depicted in FIG. 3G, is an optional surface treatment 34of the pattern transferred into the planarization layer 22 that willimpact the self-assembly of the BCP. As described below in more detail,this treatment is needed in some cases and is not needed in other cases.Further, the surface treatment can effect a change in surface propertiesof certain surfaces while leaving other surfaces unchanged. For example,as depicted in FIG. 3G, the surface treatment 34 can alter the exposedsurface portions 36 of the lines 10, while leaving the sidewalls 40 andbottom surfaces 42 of the template 30 unchanged.

After this optional surface treatment, a BCP 50 is applied to thepattern, as shown in FIG. 3H to fill the template 30 (partially orcompletely), and then annealed allowing the BCP to form a cylindricalmorphology, as shown in FIG. 3I. More specifically, the anneal causes afirst block 52 of the BCP to form a plurality of cylinders 32 alignedover the lines 10 within a matrix of a second block 54 of the BCP.Subsequent development of the BCP 50 to remove the cylindricalmorphology, i.e., the first block 52 of the BCP 50, as shown in FIG. 3J,gives access to the topography 20 by exposing the DSA patternimmediately overlying the topography 20. There is then access to makethe appropriate cuts of the underlying array of lines 10, as shown inFIG. 3K, so etching can be done and selected lines 10 cut, as thecircuit design requires, to form a patterned topography. The substrate18 is then stripped to reveal the patterned topography, i.e., an array60 of cut lines 10′, as shown in FIG. 3L.

For the process flow of FIGS. 3A-3L to be optimized, there are a host ofvariables that can be leveraged. Specifically, the shape of the template30 and how the topography 20 is aligned in that template 30, as well asthe surface energies of the different surfaces can be adjusted.Therefore, this approach is a combination of chemo- and grapho-epitaxy.The importance of the chemo-epitaxy in this approach can be seen througha simulation study that was completed using a Monte Carlo code. The areadepicted in FIG. 2, shown in perspective view in FIG. 4, was used forthe simulation, and the BCP 50 was polystyrene/polymethyl methacrylate(PS/PMMA), with the PMMA block forming the cylindrical morphology.

In the simulation study, the parameters that were plotted are surfaceinteraction parameters, which are presented on a normalized 0-2.0 scalethat represents the full degree of wetting that may be observed in thesystem. Λ_(s) refers to the interaction between the PMMA block of theBCP 50 and the sidewall 40 of the template 30 in normalized simulationunits; Λ_(T) refers to the interaction between the PMMA block of the BCP10 and the topography 20. There is a third interaction, Λ_(b), thatdescribes the interaction between the PMMA block of the BCP and thebottom surface 42 of the template. Λ_(b) was kept constant for the setof simulations at a value of 1.0. The pictures in FIG. 5 were takenalong line 5-5 of FIG. 2, and are the perspective of one looking at thejunction of the V. The cylinder in the middle, 32 _(M), is located atthe junction, and the cylinders at the left and right, 32 _(L) and 32_(R), respectively, are located at the end of each arm of the template.It is clear that controlling the chemical nature of the surfaces has alarge impact on the type of assembly that is observed. For example, inthe point at Λ_(T)=0.2 and Λ_(s)=1.0, it can be seen that all threecylinders, 32 _(L), 32 _(M), and 32 _(R), connect from the surface ofthe BCP 50 to the topography 20 itself. There are also parallelcylinders 33 that connect these three vertical cylinders 32 _(L), 32_(M), and 32 _(R) together. This type of three-dimensional structure canbe used to cut features such as gates. In a first step, the PMMA couldbe etched out through the use of a RIE etch step, and a second etch stepcould then be used to cut the lines. On the other hand, viewing thesimulation results where Λ_(T)=2.0 and Λ_(s)=0.2, none of the threecylinders 32 _(L), 32 _(M), and 32 _(R) are contacting the topography20. Finally, in the simulation where Λ_(T)=2.0 and Λ_(s)=1.6, it can beseen that the cylinder 32 _(M) at the junction of the V is connected tothe topography 20, but the other two cylinders, 32 _(L) and 32 _(R), arenot. For these last two conditions, transfer of the pattern to cut thelines 10 could be difficult because all three of the cylinders 32 _(L),32 _(M), and 32 _(R) are not open to the topography 20.

The simulation study also illustrates that having too high of a positiveinteraction on the topography 20 can lead to a disconnected cylinder 32.In these cases, a wetting layer of PMMA forms on top of the topography20, but does not connect fully with the cylinder 32. Thoughcounter-intuitive, one can imagine the situation where the very highattraction between this phase of the BCP and the topography causes atension in the cylinder (akin to pulling a piece of gum). The BCP hassome elasticity and can stretch if this tension is not too great, but ifit is, then the cylinder breaks and forms two different pieces—onewetting the topography, and one hovering in the majority phase,disconnected from the topography.

The simulation study depicted in FIG. 5 thus illustrates the importanceof chemo-epitaxy on the formation of the structures within the V-shapedtemplate. The importance of grapho-epitaxy in this scenario isillustrated by comparing a case where the topography in the template isremoved.

As shown in FIG. 6A, the structure formed without topography has anadditional two cylinders branching out of the cylinder 32 _(M) locatedat the V of the template 30, whereas the template 30 with the topography20, shown in FIG. 6B, has two cylinders 32 _(L) and 32 _(R) attached tothe topography and one cylinder 32 _(M) that does not connect. The addedvolume of the template left by the topography allows the minority phaseof the BCP to have more room to form this complicated geometry and so itdoes.

Finally, the present disclosure addresses means for effecting differentchemical interactions on the different surfaces. The simulation studiesillustrate that the interaction at the bottom surface 42 (i.e., at ornear the interface with the substrate 18) is not very critical whenthere is topography 20 within the template 30. The simplest way toimpart the necessary surface properties on the sidewall 40 of thetemplate and on the topography, i.e., on the surfaces of the lines 10,is for the materials selected to have these conditions naturally. So, increating such structures, materials are selected for the topography andthe template that have different surface properties and can be used tomanipulate the geometry. Therefore, the chemo-epitaxy aspect of theinvention may be achieved through material selection, making a surfacetreatment step unnecessary. Alternatively, if the structures are notselected with the desired properties, there are a variety of processsteps that can be used to change the surface properties after creationof the template.

One method for altering the surface properties is the use of liquidrinses. Acid rinses may be used, with a subsequent bake step causingacid catalyzed deprotection of a surface (while leaving the othersurfaces intact). This would provide control of the polarity of asurface. By way of example and not limitation, acid rinses may includelow concentrations of strong acids such as HCl, H₂SO₄, HNO₃, HSO₃F, orfluorine-based acetic acids at pH>2. Weak acids like acetic acid mayalso be used, again maintaining a pH>2. One skilled in the art mayappreciated that other acid solutions may used provided they are notdetrimental to the hardware used in the processing system. Basic rinses,such as common photoresist developer, may be used to change the contactangle of one or more surfaces. By way of example and not limitation,Basic rinses may include tetramethyl ammonium hydroxide (TMAH),specifically at standard developer concentrations (0.26N), tetra-butylammonium hydroxide, tertiary amines (e.g., trioctyl amine) or secondaryamines. Solvent rinses may be used, which can potentially solubilize andremove small molecular weight compounds that exist in or near thesurfaces. By way of example and not limitation, solvents may includepropylene glycol methyl ether acetate (PGMEA), ethyl lactate, n-butylacetate, gamma butyrolactone, cyclohexanone, or 2-heptanone (methyl amylketone). Cleaning rinses may be used, including standard chemistry usedin the industry to prepare surfaces for further processing inmicroelectronics. The cleaning rinses can change the surface propertiesof the interfaces. By way of example and not limitation, suchchemistries include dimethyl sulfoxide (DMSO), TMAH, DMSO+TMAH(Orgasolv™), SC1 (40 parts deionized water, 1 part hydrogen peroxide, 1part ammonia hydroxide), SC2 (160 parts deionized water, 4 partshydrogen peroxide, 1 part hydrochloric acid), monomethyl ether acetate(MEA), and DMSO+MEA. Reactive rinses may be used, which can react with asurface to change the nature of the surface. One example is a silylatingagent that reacts with free acidic OH groups to leave a silicon groupattached to the surface. For example, a liquid hexamethyldisilazane(HMDS) treatment may be used.

Another method for altering the surface properties is the use of brushcoatings polymers, which can be coated on the template structure tochange the surface to either polar or non-polar. These brush coatingscan be modified so that they can selectively graft to one surfacewithout grafting to another surface. The excess can be rinsed to removethe non-grafted brush from one or more of the surfaces of interest. Byway of example and not limitation, the brush coating may comprise onephase of the BCP, advantageously with a hydroxyl termination, such asOH-terminated PMMA or OH-terminated PS.

Other methods for altering the surface properties include the use of UVtreatment or ozonation. Some materials will undergo chemical and surfacechanges in the presence of deep UV (DUV) radiation. Such chemicalchanges can be used to change the surface energy of a substrate. DUVplus heat can cause cross-linking of organic materials. Ozonation, whichis UV treatment with oxygen, tends to oxidize surfaces to make them morehydrophilic. Ozonation can be completed by generating ozone in situ(oxygen+172 nm light) in the presence of the substrate, through the useof ozonated water, or direct treatment with ozone itself.

Other methods for altering the surface properties include the use ofplasma treatments, direct current superposition (DCS) cure, electronbeam (E-Beam) curing, and gas cluster ion beam (GCIB) treatment. Plasmatreatments can be used to generate radicals, which can react withsurfaces and change their properties. They can also be used to createpolymers which will deposit on the wafer. Treatment with DCS also formsan oxidized surface. DCS is both a cross-linking (curing) and SiO₂deposition method. DCS is conducted in a capacitively coupled plasma(CCP) reactor where a negative DC voltage is imposed upon a top siliconelectrode, and the negative voltage superposition accelerates ions fromplasma towards the top electrode resulting in high energyion-bombardment on the top electrode. Secondary electrons are therebyproduced which become ballistic upon being accelerated through the DCsheath. Ion-bombardment also causes physical sputtering of Si from thetop electrode. Both the ballistic electrons and the sputtered Si raindown upon the substrate sitting on the bottom electrode. The thin Sicoating formed on the substrate is then instantaneously oxidized uponexposure to air/moisture. E-Beam curing can cause surface changessimilar to oxidative changes. In a GCIB treatment, ions can attackhorizontal surfaces while leaving vertical surfaces unchanged. In somecases, polymers can be deposited on horizontal surfaces as well.

Another method for altering the surface properties is the use of gastreatments. Reactive vapors, like HMDS or other vapor silylating agents,can graft to some surfaces and change the contact angle (akin to theliquid reactive rinse with HMDS discussed above, but in gas phase).

Another method for altering the surface properties is the use ofsequential infiltration synthesis (SIS) treatment, which is a means ofdoing sequential gas or liquid treatments to grow units on and in amaterial, one reaction at a time. The reactions tend to work from theoutside in. Argonne National Labs has a SIS treatment system that usestrimethyl aluminum as the critical agent, which reacts with ester groupsto incorporate aluminum into a film.

Assuming that the materials are different, some of the surface-alteringprocessing above will have a natural selectivity that can thus result inselective changes in surface energy. In other cases, the presence ofreactive sites at the surface of one material or another can allow forselective incorporation of a surface-changing material.

Although simulations have not shown a strong dependence on the chemicalactivity of the bottom surface 42 of the template, it is possible toenvision situations where that surface does come into play. In thatcase, for example, sequential treatments of the template where oneprocess is designed to treat the topography and one process is designedto treat the bottom of the template may be used. As an example, in afirst step, the template is treated with a first brush polymer that canonly graft to the topography, followed by a rinse to remove any excess,and in a second step, the template is treated with a second brushpolymer that can only graft to the bottom of the template, followed by arinse to remove any excess. Furthermore, there are cases where thetopography might have the desired chemical activity, and so treatment ofthe bottom alone would be required. Therefore, the processes listedabove to help create a difference in chemical activity between thesidewall and the topography can also be used to create differences inthe template bottom as well.

While embodiments of the invention have been described with reference toan example of attaching a DSA pattern to an existing topographycomprising an array of lines to be cut, the method is also applicablewith little modification for attachment of a DSA pattern to any kind oftopography, whether in a regular array, or not, as long as the templateis formed for the grapho-epitaxy aspect, and as long as the appropriatechemical activity is inherently possessed by the template, topography,and bottom for the chemo-epitaxy aspect, either inherently or throughsurface treatment. In the latter aspect, as described above, variouschemical treatments can be used to alter the chemical activities of anyor all of the template, topography, and bottom, to facilitateself-assembly immediately on top of the existing topography.

In a second embodiment, the same concepts described above in referenceto FIGS. 3A-3L are applicable for a different purpose. Consider the casewhere it is desired to use a graphical trench to drive the assembly of aseries of contact holes. Such an application can include any number ofcontacts within a narrow trench, and can also be extended to cases wherethe trench has turns (like T's or L's). Prior work on this kind ofapplication has revealed a shortcoming in that the holes are notperfectly placed as desired, with respect to the underlying topography.The prior work shows that placement error of two holes in the templateis approximately 1.0 nm in the short axis and 1.3 nm in the long axis,and as the trench gets longer and longer, the image placement in theshort axis stays relatively constant, but the offset in the long-axiscontinues to increase. The implication is that where the holes arewell-confined (i.e., the short axis), their placement is better thanwhen they have additional freedom to move (i.e., the long axis). Sincethe placement of patterns is as critical as the dimension of thefeature, there is concern that the tendency of these cylinders to shiftwithin the templates may make it difficult to bring this technology tohigh-volume manufacturing.

The present invention solves this issue by placing a topography 20within the template 30, and using it to tether the cylindrical phases 32of the BCP 50 in place, as shown in FIG. 7. The graphical template 30will maintain the placement of the contact holes in the narrowdirection. By appropriate treatment of the topography 20, the chemicalinteraction will maintain the placement of the contact holes in the longaxis of the template 30 (or near infinite axis in the case of a longtrench with contact holes.)

One benefit of this approach is that the resulting structure (holes 16making contact to lines 10) is a standard structure for contacts andgates or via and trenches, and the invention facilitates theconstruction of a needed component.

Another variant of this embodiment will occur where the layout dictatesthat there are not lines 10 for every single hole in the trench. In thiscase, the chemically modified topography 20 will still drive theplacement of the contact holes that will make contact with thetopography 20, i.e., lines 10, while the holes without the topography 20will still be more constrained than they would be in the case withoutthe chemically active topography 20, but will still have more error intheir placement than those that are tethered. These non-contacting holescould be left as is (i.e., dummy holes). Alternatively, as depicted inthe process flow FIGS. 8A-8C, these holes could be removed through asecond patterning step where only the desired contact holes are openedin the second patterning step. FIG. 8A shows the template 30 formed overthe topography 20, which includes a plurality of spaced lines 10. FIG.8B depicts the result of the DSA process of the invention, with thecylinders 32 a of the BCP 50 that correspond to the contact holestethered to the lines 10 and the cylinders 32 b that correspond to thenon-contact holes not tethered to any underlying topography but stillconstrained within the template 30. FIG. 8C depicts the creation of amask 70 for patterning the contact holes from the cylinders 32 a.

For embodiments of the invention, there are control parameters thataffect the generation of structures. Template shape parameters includesthickness, distance and slope. The template thickness may be on theorder of 50-800 nm, for example. By way of further example, the templatethickness may be on the order of 50-100 nm, but may in some cases varyup to 600-800 nm. In the embodiment described above in FIGS. 3A-3L, thematerial comprising the template 30 is also the bottom layer of adual-layer ARC, and so the thickness selected must also serve tominimize reflectivity. The distance parameter is the distance that thetemplate comes in proximity to the desired locations of the contactholes (e.g., 1.8-2.5 L_(o), where L_(o) is the characteristic length ofthe BCP). The slope parameter refers to the sidewall slope of thetemplate, for example, 80-90 degrees.

Topography shape parameters include height, width and slope. Thetopography height may be on the order of 1-25 nm, for example. By way offurther example, the topography height may be 10-20 nm, or 15-25 nm, oraround 15 nm. The topography width may be on the order of 15-25 nm, forexample. The slope parameter refers to the sidewall slope of thetopography, for example, 80-90 degrees.

Other control parameters relate to surface characteristics. The chemicalactivity of the template sidewall may be on the order of 0.2-1.6 J/cm²,for example. The chemical activity of the topography may be on the orderof 0.1-0.5 J/cm², for example. The chemical activity of the bottomsurface of the template may be on the order of 0.2-2.0 J/cm², forexample.

Other control parameters relate to the BCP. The percentage of theminority block of the BCP may be 25-40%, for example. The characteristiclength, L_(o), of the BCP is specifically selected to give the size ofhole that is desired for a particular application, i.e., the target sizeof the contact hole. χN of the BCP (product of chi parameter with degreeof polymerization) may be on the order of 15-30 for PS/PMMA BCPs. As theχ of the BCP increases, it allows for a lower N to be used and stillremain above the order/disorder transition. Lower N then translates tosmaller features. The range quoted is based on the simulations done withPS/PMMA BCPs. For higher χ BCPs, the value for χN might exceed thisrange. The fill height of the BCP within the template may be on theorder of 50-100%, for example, 70-100%, 70-90%, or 80-100%.

Since the invention utilizes both grapho- and chemo-epitaxy to drive theassembly of the block copolymer, a balance between the two drivingforces is required. The template shape and topography shape dictate howmuch volume there is for the BCP to fill, and this will change as thestructure of interest changes. The degree of chemo-epitaxy required willdepend on how much grapho-epitaxy impetus is present, and so it too willdepend on the geometry of the shape under consideration. Ultimately, itis believed that the volume of the shape, the percentage of the minorityphase in the block copolymer, the L_(o) of the block copolymer and theheight above the template are related by a thermodynamic phenomenon andcan be optimized to give the desired “graphical influence.” The“chemical influence” needed will then be based on that. The V-shapedsimulations discussed above provide an indication of the usable rangesfor the control parameters, which are provided above by way of examples,but not limitations.

As described above, one of the methods for creating the template 30 isto etch it into the planarization layer 22 of a dual layer BARC 26,which planarization layer is typically a spin-on carbon film, or a CVDalpha-carbon film. In either case, it is largely organic, and etchtransfer into this organic film is accomplished with anoxygen-containing etch process. The use of oxygen in this step leavesthe exposed surfaces oxidized, which in turn makes them hydrophilic andpreferentially favorable to wetting by PMMA in a PS-PMMA blockcopolymer.

Because the surfaces (sidewalls, topography, and trench floor) are sofavorable for PMMA-wetting, most of PMMA in the BCP goes to wet thesesurfaces, and relatively little material is available for the formationof the morphology that would connect to the topography 20. Thus, inaccordance with an embodiment of the invention, if the surfaces areshifted to a weaker PMMA wetting condition, the morphology changesdramatically by making more PMMA available to connect to the topography20. Specifically, there is less PMMA along the sidewalls, and moreavailable to form the connected morphology within the center of thetemplate 30. This morphology has individual access points to thetopography 20 through the PMMA structure, and with some engineeringduring the etch transfer, this morphology can be used to individuallycut the lines 10 that are accessed through the connection.

In accordance with one embodiment using chemo-epitaxy in combinationwith grapho-epitaxy, a method to create a template 30 that has thislow-wetting characteristic includes reverting to the natural state ofthe template 30 after the transfer etch (that uses oxidizing agent) to aless oxidized condition. One implementation is to change etch gases inthe chamber to a more reductive chemistry, strike a plasma with lowbias, and allow the plasma to bring the oxidative surface back toward amore neutral state (but still PMMA-wetting to a low degree). One exampleof a reducing chemistry is H₂. The H₂ plasma could be used, for example,during the over-etch. The reducing plasma can also be accomplished bymoving to a separate chamber where the reducing plasma is struck.Reverting to the less oxidized condition can also be completed throughwet processing. The wet chemical would likewise need to have reducingcapability. While reductive chemistry is more difficult to accomplish inwet systems, since wet systems generally use aqueous delivery methodsthat typically include a lot of dissolved oxygen, it is conceived thatHF can be used as a reducing wet chemistry, although it would have to bedilute to avoid destruction of the template or the underlyingtopography.

In an alternative embodiment, rather than treating the surfaces to makethem less PMMA-wettable, the surfaces are treated to make themPS-wettable, i.e., the polarity is reversed. In accordance with thisembodiment, the interior of the template 30 is coated with a PS—OH brushmaterial. This brush can graft itself to the hydrophilic surface via theOH-portion, and the PS-portion of the polymer points away from the graftto give a PS-wettable surface. Then, when a PS-PMMA BCP is applied tothe template 30, it is wetted by a PS layer instead of a PMMA layer.Fundamentally, this allows for all of the PMMA in the BCP to go towardcreation of the morphology that will cut the lines 10.

Simulations were completed to determine the impact of changing thesurface in this way. Energetically, the PMMA-PS-surface interaction wasnegative, and this resulted in a repulsion between the surfaces and thePMMA domain. Therefore, the PMMA domain rose over each line 10 of thetopography 20 and tried to nestle itself between the lines 10 withouttouching them. This dual behavior, in addition to a repulsion from thesidewalls, led to self alignment of this structure over the topography.Fortuitously, the resulting topography in this scenario is such that themorphology opens to the air above each of the lines. The PMMA can thenbe wet developed out of this structure by first exposing to UV-light,and then applying a suitable organic solvent, as may be determined bypersons of ordinary skill in the art. By way of example and notlimitation, suitable solvents may include acetone, methanol, methylethyl ketone, methyl isobutyl ketone, 2-heptanone, n-butyl acetate,gamma butyrolactone, ethyl lactate, and PGMEA. Next, a directional etchcan be used to use the open access points to cut the lines 10, and thecuts that are made will be more precise than could be made with thelithographical template alone. This provides for end to end spacing oflines that is more compact and favorable for transistor packing onsilicon.

In practice, there are various paths of implementation for applicationof the PS—OH brush and its grafting to the surfaces. However, theimplementation should take into account that the sidewalls, bottomsurface, and topography may all be created out of different materials,which affects the wetting and grafting of the PS—OH brush to thedifferent material surfaces. One method for applying the brush to thesurfaces that have different material compositions is using a DCS cure.This process applies a very thin layer of silicon on top of allsurfaces. That silicon layer is then oxidized by exposure to air ormoisture. Oxidation may alternatively be accomplished with a plasma, byan in-situ ozonation created with 172 nm light+oxygen, or by a wetprocess where ozone is bubbled through water and applied to the wafer asan oxidation agent. TMAH-based photoresist developer may also be used tocreate terminating hydroxyl groups on the silicon surfaces. Thistreatment creates a more uniform hydroxy-terminated surface that canthen be more uniformly “polarity-reversed” as the PS—OH brush is graftedto it.

While the present invention has been illustrated by a description of oneor more embodiments thereof and while these embodiments have beendescribed in considerable detail, they are not intended to restrict orin any way limit the scope of the appended claims to such detail.Additional alternatives, advantages and/or modifications will readilyappear to those skilled in the art. For example, it may be possible tocontrol the template topography and surfaces so that the cylinders landbetween the topographic lines instead of on top of them. Also, similarto the first disclosed embodiment, the application of the above methodcan be envisioned for use in situations other than attachment andcutting of an array of lines. The invention in its broader aspects istherefore not limited to the specific details, representative apparatusand method, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thescope of the general inventive concept.

What is claimed is:
 1. A method for forming a patterned topography on asubstrate, comprising: providing a substrate with features formed atop,the features forming an existing topography; forming a template fordirected self-assembly (DSA) immediately atop the topography, thetemplate comprising exposed template surfaces surrounding regions ofexposed topography; treating the exposed template surfaces to alter atleast one surface property thereof; filling the template with a blockcopolymer (BCP) to cover the exposed topography; annealing the blockcopolymer (BCP) within the template to drive self-assembly in alignmentwith the topography; and developing the annealed block copolymer (BCP)to expose a directed self-assembly (DSA) pattern above the topography.2. The method of claim 1, wherein the step of forming the templatecomprises a plasma etching step using a first plasma comprising oxygen.3. The method of claim 2, wherein the step of treating the exposedtemplate surfaces comprises exposing the template to a second plasmadifferent than the first plasma.
 4. The method of claim 3, wherein thesecond plasma comprises hydrogen.
 5. The method of claim 1, wherein thestep of treating the exposed template surfaces renders the exposedtemplate surfaces less attractive to one phase of the block copolymer(BCP) compared to the exposed template surfaces prior to the treatment.6. The method of claim 1, wherein the step of treating the exposedtemplate surfaces comprises exposing the template to a wet processingchemistry.
 7. The method of claim 6, wherein the wet processingchemistry comprises dilute hydrogen fluoride.
 8. The method of claim 1,wherein the block copolymer (BCP) comprises polystyrene (PS) and polymethyl methacrylate (PMMA).
 9. The method of claim 1, furthercomprising: transferring the directed self-assembly (DSA) pattern intothe topography, to form a patterned topography.
 10. A method for forminga patterned topography on a substrate, comprising: providing a substratewith features formed atop, the features forming an existing topography;forming a template for directed self-assembly (DSA) immediately atop thetopography, the template comprising exposed template surfacessurrounding regions of exposed topography, wherein forming the templatecomprises plasma etching with an oxygen-containing plasma whereby theexposed template surfaces are oxidized; treating the exposed templatesurfaces with a hydrogen-containing reducing chemistry to alter theexposed template surfaces to a less oxidized state; filling the templatewith a block copolymer (BCP) to cover the exposed topography; annealingthe block copolymer (BCP) within the template to drive self-assembly inalignment with the topography; developing the annealed block copolymer(BCP) to expose a directed self-assembly (DSA) pattern above thetopography; and transferring the directed self-assembly (DSA) patterninto the topography, to form a patterned topography.
 11. The method ofclaim 10, wherein the block copolymer (BCP) comprises polystyrene (PS)and poly methyl methacrylate (PMMA), wherein the poly methylmethacrylate (PMMA) is attracted to oxidized surfaces such that the polymethyl methacrylate (PMMA) is less attracted to the treated exposedtemplate surfaces having the less oxidized state than to the untreatedexposed template surfaces.
 12. A method for forming a patternedtopography on a substrate, comprising: providing a substrate withfeatures formed atop, the features forming an existing topography;forming a template for directed self-assembly (DSA) immediately atop thetopography, the template comprising exposed template surfacessurrounding regions of exposed topography; coating the exposed templatesurfaces with a first phase of a block copolymer (BCP) to render theexposed template surfaces more attractive to the first phase of theblock copolymer (BCP) than prior to the coating; filling the templatewith the block copolymer (BCP) to cover the topography; annealing theblock copolymer (BCP) within the template to drive self-assembly of theblock copolymer (BCP) with a second phase of the block copolymer (BCP)in alignment with the topography; and developing the annealed blockcopolymer (BCP) to expose a directed self-assembly (DSA) patternimmediately above the topography.
 13. The method of claim 12, furthercomprising: performing a direct current superposition (DCS) treatment ofthe exposed template surfaces prior to coating the exposed templatesurfaces with the first phase of the block copolymer (BCP).
 14. Themethod of claim 12, further comprising: exposing the exposed templatesurfaces to an oxygen-containing environment prior to coating theexposed template surfaces with the first phase of the block copolymer(BCP).
 15. The method of claim 14, wherein the oxygen-containingenvironment is an oxygen-containing plasma or ozone.
 16. The method ofclaim 12, further comprising: exposing the exposed template surfaces toa wet processing chemistry comprising tetramethyl ammonium hydroxide(TMAH) prior to coating the exposed template surfaces with the firstphase of the block copolymer (BCP).
 17. The method of claim 12, whereinthe first phase of the block copolymer (BCP) is polystyrene (PS) and thesecond phase is poly methyl methacrylate (PMMA).
 18. The method of claim12, further comprising: transferring the directed self-assembly (DSA)pattern into the topography, to form a patterned topography.
 19. Amethod for forming a patterned topography on a substrate, comprising:providing a substrate with features formed atop, the features forming anexisting topography; forming a template for directed self-assembly (DSA)immediately atop the topography, the template comprising exposedtemplate surfaces surrounding regions of exposed topography; performinga direct current superposition (DCS) treatment of the exposed templatesurfaces to apply a layer of silicon to the exposed template surfaces;exposing the layer of silicon on the exposed template surfaces to anoxygen-containing environment to oxidize the exposed template surfaces;coating the oxidized exposed template surfaces with a brush polymer ofOH and a first phase of a block copolymer (BCP) to render the exposedtemplate surfaces more attractive to the first phase of the blockcopolymer (BCP) than prior to the coating; filling the template with ablock copolymer (BCP) to cover the exposed topography; annealing theblock copolymer (BCP) within the template to drive self-assembly of theblock copolymer (BCP) with a second phase of the block copolymer (BCP)in alignment with the topography; developing the annealed blockcopolymer (BCP) to expose a directed self-assembly (DSA) patternimmediately above the topography; and transferring the directedself-assembly (DSA) pattern into the topography, to form a patternedtopography.
 20. The method of claim 19, wherein the first phase of theblock copolymer (BCP) is polystyrene (PS) and the second phase is polymethyl methacrylate (PMMA).